This invention relates to polycarbonate, and the production thereof, where a chain terminator has been utilized in the manufacturing process, and to molded articles such as compact discs made from such polycarbonate.
It is known to produce polycarbonate by the reaction of a dihydroxy compound, particularly an aromatic dihydroxy compound such as the diol Bisphenol-A, with a derivative of carbonic acid, such as phosgene. A chain terminator is often added to the reaction mixture for the purpose of regulating the molecular weight of the polycarbonate product. When used, the prevalent practice in the art is to include the chain terminator in the monomer mix which is initially charged to the reaction vessel. The dihydroxy compound and the chain terminator are consequently both present in the reaction mixture when it is contacted with the carbonic acid derivative.
In the manufacture of polycarbonate as described above, molecules of varying degrees of polymerization are obtained. The chain terminator is useful for the purpose of attempting to confine a large percentage of the molecules to a preselected molecular weight range. However it has been found that, even when a terminator is used according to the practice in the art as described above, not all molecules conform to the preselected weight range, and some molecules of extremely low molecular weight (carbonate byproducts) can still result.
Carbonate byproducts, being the smallest of the molecules resulting from the production of polycarbonate, have the lowest respective boiling points and are therefore the most likely to exist in vapor phase. The presence of carbonate byproducts in vapor phase becomes a consideration when polycarbonate is, for example, being extruded or molded, or heated for any other purpose. Accordingly, it would be desirable to prevent or limit the formation of carbonate byproducts in polycarbonate, and thereby assist in the manufacture of a polycarbonate product wherein the greatest possible percentage of the molecules fall within the preselected molecular weight range which it is the purpose of the terminator to achieve.